Field of the Invention
The present invention relates to a photoelectric conversion device, a method of manufacturing the same, and a camera.
Description of the Related Art
If a metal impurity is mixed into a pixel portion in the manufacturing process of a solid-state image sensor, an increase in dark current of a photoelectric conversion element and occurrence of a white defect are caused. Mixture of the metal impurity into the pixel portion can be caused not only by a manufacturing apparatus but also by thermal diffusion of a silicide material used for a peripheral circuit portion. Japanese Patent Laid-Open No. 10-41311 is related to a gettering technique in a solid-state image sensing element. Japanese Patent Laid-Open No. 10-41311 describes obtaining a gettering capability by ion-implanting carbon and oxygen in a silicon substrate. Japanese Patent Laid-Open No. 10-41311 also describes that it is desirable that an oxygen peak concentration is set equal to or higher than a carbon peak concentration, and oxygen and carbon are made equal to each other in projection range after ion implantation in order to obtain a strong gettering capability by effectively forming a compound of oxygen and carbon.
However, if oxygen is implanted in the silicon substrate intentionally, oxygen that diffuses into an epitaxial layer in an annealing process or the like during the manufacturing process increases. This may induce a crystal defect owing to oxygen in a region close to a pixel. In particular, when a metal such as Co or Ni whose diffusion rate is high in silicon in a low temperature is used, it is desirable that the crystal defect in the epitaxial layer close to the pixel is suppressed, and the metal is captured in a gettering layer formed in the region as deep as possible.
If an oxygen concentration in the silicon substrate is high, or if oxygen is ion-implanted intentionally in the silicon substrate, it is considered that not the metal to be captured but oxygen is gettered in a large amount due to a distortion caused by arranging carbon at the lattice position of silicon. This means that the effect of gettering the metal decreases. For the above-described reasons, it cannot be said that the conventional gettering technique is optimal as a method of reducing a white defect failure of the solid-state image sensor.